The medical device industry produces a wide variety of electronic and mechanical devices for treating patient medical conditions. Depending upon medical condition, medical devices can be surgically implanted or connected externally to the patient receiving treatment. Clinicians use medical devices alone or in combination with drug therapies and surgery to treat patient medical conditions. For some medical conditions, medical devices provide the best, and sometimes the only, therapy to restore an individual to a more healthful condition and a fuller life. One type of medical device that can be used is an Implantable Neuro Stimulator (INS).
An INS generates an electrical stimulation signal that is used to influence the human nervous system or organs. Electrical contacts carried on the distal end of a lead are placed at the desired stimulation site such as the spine and the proximal end of the lead is connected to the INS. The INS is then surgically implanted into an individual such as into a subcutaneous pocket in the abdomen. The INS can be powered by an internal source such as a battery or by an external source such as a radio frequency transmitter. A clinician programs the INS with a therapy using a programmer. The therapy configures parameters of the stimulation signal for the specific patient's therapy. An INS can be used to treat conditions such as pain, incontinence, movement disorders such as epilepsy and Parkinson's disease, and sleep apnea. Additional therapies appear promising to treat a variety of physiological, psychological, and emotional conditions. As the number of INS therapies has expanded, greater demands have been placed on the INS. Examples of some INSs and related components are shown and described in a brochure titled Implantable Neurostimulation Systems available from Medtronic, Inc., Minneapolis, Minn.
The effectiveness of the therapy as provided by the INS is dependent upon its capability of adjusting the electrical characteristics of the stimulation signal. For example, stimulation waveforms can be designed for selective electrical stimulation of the nervous system. Two types of selectivity may be considered. First, fiber diameter selectivity refers to the ability to activate one group of nerve fibers having a common diameter without activating nerve fibers having different diameters. Second, spatial selectivity refers to the ability to activate nerve fibers in a localized region without activating nerve fibers in neighboring regions.
The tissue around a first stimulated electrode can be damaged by a charge accumulation. Thus, a recharging interval is typically utilized to balance a charge accumulation that may occur around the surrounding tissue of the first stimulated electrode. A time delay between a stimulation pulse and the recharging interval may be required in order to prevent a loss of potential in adjacent tissue. The potential may be associated with a second stimulated electrode that is being stimulated by a different stimulation pulse than the first stimulated electrode. A capacitive element may be utilized for each regulator module or each stimulation electrode. In the event that discharging and recharging is uneven, the capacitive element builds up a charge potential that absorbs the charge imbalance.
This capacitive element, however, is susceptible to failure. For example, the capacitive element may become shorted or opened. When the capacitive element fails, the corresponding electrode may no longer be able to adequately delivery electrical stimulation.
The patient or physician, however, will not know whether the capacitive element has failed and that the device is not performing as expected. The patient/physician may, for example, incorrectly diagnose that the treatment therapy is not working. Even if it is determined that the device is not performing as required, the physician may not know what specifically is causing the problem. As a result, the patient may have to endure another surgical procedure to repair or replace the device.
Even if it can be readily determine that the device is not performing as required, the physician must still meet with the patient to determine how to resolve the problem. The physician may have to contact the device manufacturer to help resolve the problem. Until the physician can properly treat the problem, however, the patient may have to endure a time period where he/she is receiving inadequate treatment therapy.
It is therefore desirable to readily determine when a capacitive element has failed and to correct for the failure without requiring the patient to endure a surgical procedure.